1. Field of the Invention:
This invention relates to a cardiac output measurement system used in examining cardiac function.
2. Description of the Prior Art:
In order to measure cardiac output by the right heart catheter method for the purpose of examining cardiac function, the conventional practice is to employ an indicator attenuation method. Let us describe thermal attenuation, which is one of the indicator attenuation methods available, while referring to FIG. 1.
According to the right heart catheter method, a catheter 25 is introduced from a pnathic vein, femoral vein or elbow vein and is passed through the superior or inferior vena cava, the right auricle RA and the right ventricle RV to position its distal end in the pulmonary artery. The catheter 25 includes a charge port 26 and a thermistor 27 and is so adapted that the charge port 26 and thermistor 27 occupy positions in the right auricle RA and pulmonary artery, respectively. With the catheter 25 so disposed, a liquid the temperature of which is higher or lower than blood temperature is introduced into the heart from the charge port 26. As the liquid spreads through the right auricle RA and right ventricle RV, the temperature of the liquid is attenuated. The attenuated temperature of the liquid is sensed by the thermistor 27 in the pulmonary artery, allowing cardiac output to be calculated from the area of the attenuation curve (change in temperature with time, as shown in FIG. 2) in accordance with the following Eq. (1), developed by Stewart Hamilton: ##EQU1## where C.O: cardiac output,
Si: specific gravity of injected liquid, PA1 Ci; specific heat of injected liquid, PA1 Vi: amount of injected liquid, PA1 Ti: temperature of injected liquid, PA1 Tb: temperature of blood, PA1 Sb: specific gravity of blood, PA1 Cb: specific heat of blood, ##STR1## area of attenuation curve
A disadvantage of the conventional cardiac output measurement system which relies upon an indicator attenuation method such as the above-described thermal attenuation method is that measurement of cardiac output is performed intermittently and not continuously. Moreover, when it is attempted to perform measurement frequently, the total amount of injected liquid assumes large proportions, therby submitting the patient to a considerable burden. Another problem is increased risk of infection.